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Call sign
Series of unique letters and numbers assigned to a person who has earned an Amateur Radio license.

Capacitance
A measure of the ability of a capacitor to store energy in an electric field.

Capacitor
An electrical component usually formed by separating two conductive plates with an insulating material. A capacitor stores energy in an electric field.

Centi
The metric prefix for 10 - 2, or divide by 100.

Chassis ground
The common connection for all parts of a circuit that connect to the negative side of the power supply.

Chirp
A slight shift in transmitter frequency each time you key the transmitter.

Closed repeater
A repeater that restricts access to those who know a special code.

Closed, or complete circuit
An electrical circuit with an uninterrupted path for the current to follow. Turning a switch on, for example, closes or completes the circuit, allowing current to flow.

Coaxial cable
Coax (pronounced ko-aks). A type of feed line with one conductor inside the other.

Color code
A system in which numerical values are assigned to various colors. Colored stripes are painted on the body of resistors and sometimes other components to show their value.

Conductor
A material that has a loose grip on its electrons, so an electrical current can pass through it.

Connected
The condition in which two packet-radio stations are sending information to each other. Each is acknowledging when the data has been received correctly.

Continuous wave (CW)
Morse code telegraphy.

Control operator
An amateur operator designated by the licensee of a station to be responsible for the transmissions of an amateur station.

Control point
The locations at which the control operator function is performed.

Controlled environment
Any area in which an RF signal may cause radiation exposure to people who are aware of the radiated electric and magnetic fields and who can exercise some control over their exposure to these fields. The FCC generally considers amateur operators and their families to be in a controlled RF exposure environment to determine the maximum permissible exposure levels.

Core
The material used in the center of an inductor coil, where the magnetic field is concentrated.

Courtesy tone
A tone or beep transmitted by a repeater to indicate that it is okay for the next station to begin transmitting. The courtesy tone is designed to allow a pause between transmissions on a repeater, so other stations can call. It also indicates that the time-out timer has been reset.

CQ
"Calling any station": the general call when requesting a conversation with anyone. Like many other telegraph terms which originated on the landlines, CQ was brought over into radio and used as a general call to all ships by the Marconi Company. Other companies used KA until the London Convention of 1912, which adopted CQ as the international general call or "attention" signal.

Crystal oscillator
A device that uses a quartz crystal to keep the frequency of a transmitter constant.

Crystal-controlled transmitter
A simple type of transmitter that consists of a crystal oscillator followed by driver and power amplifier stages.

CTCSS
Continuous tone coded squelch system. A sub-audible tone system used on some repeaters. When added to a carrier, a CTCSS tone allows a receiver to accept a signal. Also called PL.

Cubical quad antenna
An antenna built with its elements in the shape of four-sided loops. Current - A flow of electrons in an electrical circuit.

CW (Morse code)
A communications mode transmitted by on/off keying of a radio-frequency signal. Another name for international Morse code.

D region
The lowest region of the ionosphere. The D region contributes very little to short-wave radio propagation. It acts mainly to absorb energy from radio waves as they pass through it. This absorption has a significant effect on signals below about 7.5 MHz during daylight.

Data
Computer-based communications modes, such as packet radio, which can be used to transmit and receive computer files, or digital information.

DE
The Morse code abbreviation for "from" or "this is." Deci - The metric prefix for 10 - 1, or divide by 10.

Delta loop antenna
A variation of the cubical quad with triangular elements.

Detector
The stage in a receiver in which the modulation (voice or other information) is recovered from the RF signal.

Digipeater
A packet-radio station used to retransmit signals that are specifically addressed to be retransmitted by that station.

Digital communications
Computer-based communications modes. This can include data modes like packet radio and text-only modes like radioteletype (RTTY).

Dipole antenna
See Half-wave dipole. A dipole need not be 1/2 wavelength long.

Direct current (dc)
Electrical current that flows in one direction only.

Directional wattmeter
(see Wattmeter)

Director
An element in front of the driven element in a Yagi and some other directional antennas.

Double-pole, double-throw (DPDT) switch
A switch that has six contacts. The DPDT switch has two center contacts. The two center contacts can each be connected to one of two other contacts.

Double-pole, single-throw (DPST) switch
A switch that connects two contacts to another set of contacts. A DPST switch turns two circuits on or off at the same time.

Driven element
The part of an antenna that connects directly to the feed line.

Dual-band antenna
An antenna designed for use on two different Amateur Radio bands.

Dummy antenna
A station accessory that allows you to test or adjust transmitting equipment without sending a signal out over the air. Also called dummy load.

Dummy load
A station accessory that allows you to test or adjust transmitting equipment without sending a signal out over the air. Also called dummy antenna.

Duplexer
A device that allows a dual-band radio to use a single dual-band antenna.

Duty cycle
A measure of the amount of time a transmitter is operating at full output power during a single transmission. A lower duty cycle means less RF radiation exposure for the same PEP output.

DX
Distance, foreign countries.